There are many applications which require high pressure seals at an interface between adjacent differentially rotating components. In most of such applications, the differentially rotating components are coaxial with each other and have an internal fluid passageway disposed within the components. A fluid pressure differential exists between the internal fluid passageway and a region external of the differentially rotating components whereby high pressure seals are required at an interface between the components to prevent leakage of fluid between the components. If relative rotation is slow, a rubbing type seal can be held firmly against the rotating surface and is generally effective to maintain a sealing relationship, although wear and subsequent leakage are common. If, however, the relative velocity of rotation between the components is high, rubbing type seals erode too quickly and are generally ineffective and impractical in such applications.
One application in which high speed differential rotation occurs is in gas turbine engines of the type used in present day aircraft. By "differential rotation" it is meant that one apparatus rotates with respect to an adjacent apparatus. Such may occur, for example, between a stationary member and a rotating member. By way of explanation, gas turbine engines generally include a gas generator which comprises a compressor for compressing air flowing aft through the engine, a combustor in which fuel is mixed with the compressed air and ignited to form a high pressure/high temperature gas stream, and a turbine driven by the gas stream and connected for driving a rotor which in turn drives the compressor. Many engines further include a second turbine, known as a power turbine, located aft of the gas generator and which extracts energy from the gas flow to drive a rotating load such as found in the propulsor of ducted turbo-fan engines, and turbo-prop engines.
A recent improvement over the turbo-fan and and turbo-prop engine is the unducted fan engine such as disclosed in U.S. patent application Ser. No. 437,923--Johnston, filed Nov. 1, 1982, now abandoned. In the unducted fan engine, the power turbine includes counterrotating rotors and turbine blades which drive counterrotating unducted fan blades or propellers radially located with respect to the power turbine. The high pressure gas stream flows from the combustor, through a stationary duct and then through the rotors. A high pressure seal is required at the interface between the stationary duct and the adjacent rotor to prevent leakage of the high pressure gas stream.
One high pressure seal used in the past with differentially rotating members includes a forward race, an aft race, and an annular carrier. The forward race and aft race are fixedly coupled to the stationary member with an annular channel coaxial with the stationary member being defined between the forward race and the aft race. The annular carrier is coupled to the rotating member and is dimensioned to fit within the annular channel. As the rotating member rotates with respect to the stationary member, the annular carrier and races act as a low friction seal. Additionally, a small amount of leakage is permitted at the interfaces between the carrier and the races. This leakage reduces friction and subsequent wear. It is believed that one of the disadvantages of such prior art high pressure seals is excessive leakage caused by excess wear of the races and annular carrier. Any wear of the races and/or the carrier increases the gaps between the races and the carrier. An increase in the size of the gaps between the races and the carrier results in an increase in fluid leakage and, consequently, a loss in pressure. It is believed that a decrease in fluid pressure in the turbine section of a gas turbine engine reduces the efficiency of the engine.